This invention is of an apparatus for use in launching a jacket for an offshore platform for oil production purposes or any other purpose and, in particular, is for a battered leg, rather than parallel leg, jacket.
While some jackets for offshore platforms are built with special flotation chambers and towed to the location at which they will be erected, it is often more convenient to load the jacket on one or more barges for towing the jacket to location. Barges for transporting jackets for offshore platforms are discussed, for example, in the following U.S. patents: U.S. Pat. No. 3,315,473 issued to Hauber, et al., on Apr. 25, 1967; U.S. Pat. No. 3,859,806 issued to Guy, et al., on Jan. 14, 1975; and U.S. Pat. No. 3,937,027 issued to Koehler, et al., on Feb. 10, 1976.
Once a jacket loaded on the barge arrives at location, the jacket must be unloaded. Unloading techniques used for battered leg jackets in the past include partially submerging the barge, or using one or more derrick barges to lift the jacket. Both of these methods are expensive and become especially difficult with larger jackets. It has been proposed that the jacket be constructed with two parallel extra legs located between the lower battered legs (lower as the jacket is transported on the barge). The parallel legs can slide on a pair of skid rails such that the center line of the jacket will be maintained over the launching center line as the jacket moves toward (and off) the launching end of the barge. In this way, the jacket and the barge position could be maintained to avoid possible instability and damage to the barge and/or jacket. While such a system would be technically satisfactory, including two extra legs on the jacket would not be economically feasible for a wide range of water depths.